The present invention relates generally to array antennas and their fabrication methods, and more particularly, to methods of fabricating a true-time-delay continuous transverse stub array antenna.
Previous true-time-delay, continuous transverse stub array antennas were made either by machining or molding microwave circuit features out of low-loss plastics, such as Rexolite.RTM. or polypropylene. The plastic was then metalized to form a dielectric-filled, over-moded waveguide or parallel-plate waveguide structure. Such antennas are disclosed in U.S. Pat. No. 5,266,961 entitled "Continuous Transverse Element Devices and Methods of Making Same", U.S. patent application Ser. No. 08/885,583, filed Jun. 30, 1997, entitled "Planar Antenna Radiating Structure Exhibiting Quasi-Scan/Frequency Independent Driving-Point Impedance", and U.S. patent application Ser. No. 08/884,837, filed Jun. 30, 1997, entitled "Compact, Ultrawideband, Matched E-Plane Power Divider".
A prototype antenna was developed by the assignee of the present invention using the solid-dielectric approach. The prototype design operates satisfactorily over an extended band of 3.5 to 20.0 GHz. Dielectric parts of uniform cross section were made from Rexolite.RTM. 1422 using conventional machining techniques. The parts were bonded together with adhesive and then all outside surfaces except a line-feed input and the radiating aperture were metalized with a highly conductive silver paint.
The primary disadvantage of the solid-dielectric approach is the dielectric loss, which becomes increasingly significant at higher millimeter wave frequencies. Other disadvantages include variations in dielectric properties, such as inhomogeneity and anisotropy, the high cost of premium microwave dielectric materials, and to a lesser extent, the cost of fabrication, bonding and metalization of the dielectric parts. Air-dielectric designs also have problems, and in particular, microwave circuit features are internal to the waveguide structure and may be inaccessible for mechanical inspection after assembly. Thus the processes used to fabricate such antennas must insure accurate registration of parts, maintain close tolerances and provide continuous conducting surfaces across seams in waveguide walls.
Accordingly, it is an objective of the present invention to provide for methods of fabricating air-dielectric, true-time-delay continuous transverse stub array antennas.